Highly recommended, not just for Cambridge undergraduates!
Recently Tim Gowers has been looking at some sample Cambridge examination questions. But he does far more than just provide model answers. He gives some excellent general pointers as to how to think about these types of questions. For example, he addresses the issue of what you are likely to be allowed to assume as standard when you are asked to prove something. And, of course, there are some very useful general tips which should help when trying to answer not just these specific questions, but a wide range of questions of varying types.